1. FIELD OF THE INVENTION
This invention relates to an image pickup apparatus adapted for use in medical radiodiagnostics, and more particularly to a plate-shaped image pickup device for receiving a radiographic image and transforming the image into an electric signal sequence.
2. DESCRIPTION OF THE RELATED ART
U.S. Pat. No. 4,535,468 discloses a photographic apparatus for medical use with a three-layer system lying between two electrodes, to which a d-c voltage is applied. The two outer layers are photoconductors and the middle layer consists of a material in which charge carriers can be stored. An image radiated from one side can be read out from the other side in the form of an electric pulse sequence by scanning using a light beam and can be reproduced on a television screen.
U.S. Pat. No. 4,268,750 discloses an analogous photographic apparatus having a multi-layer detector including only one photoconductive layer.
The detector of these apparatuses has a pair of parallel plate electrodes sandwiching the photoconductive layer and one signal line connected thereto. The latent image once stored in the detector in the form of a charge distribution is read out as a time sequential signal by scanning a spot-shaped laser beam.
In the solid state image pickup elements, i.e. photographic sensors such as CCD cameras or MOS image pickup devices, electronic pixel selection means is adopted. This selection means is integrated on the one-chip semiconductor substrate together with the pixels. These image pickup devices, however, have extremely low sensitivity to the X ray for medical use range, and hence cannot be directly used as the X ray image pickup apparatus for medical use. Further, the image pickup apparatus for medical use requires a number of pixels as many as 4000.sup.2 at the maximum and an image plane size as wide as 40 cm .times.40 cm at the maximum. Thus, the techniques of the above-mentioned photographic image pickup devices (typically, having a number of pixels around 600.sup.2 and an image plane size of 2 inches .phi. or less) cannot be used.